1. Field of the Invention
The present invention generally relates to a tape cassette for accommodating a length of magnetic tape for the recording or reproduction of information thereon or therefrom, respectively, and, more particularly, to the tape cassette having an improved erasure preventive element.
2. Description of the Prior Art
Commercially available tape cassettes containing a reeled magnetic tape for the-recording or reproduction of analog audio signals have a basic structure comprising a generally rectangular box-like casing made up of a pair of casing halves, a length of magnetic tape, a pair of hubs to which respective opposite ends of the length of magnetic tape are secured, a plurality of guide rollers disposed along a path of travel of the length of magnetic tape from one hub to the other, shields, pads and lubricant sheets.
For avoiding any possible erroneous or premature erasure of information recorded on the length of magnetic tape, the tape cassette has a pair of breakable erasure preventive pawls 2 formed integrally with the respective casing halves 1, only one of which is shown in FIG. 6. Specifically, when one or both of the erasure preventive pawls 2 are cut away, recesses 3 defined in the casing halves and normally closed by the associated pawls 2 define detection holes, thereby providing an indication that the length of magnetic tape contained in the tape cassette should not be erased in any way.
The unique design of a pawl detecting mechanism provided in an analog audio deck requires that each of the pawls 2 serving as a detection surface must be flush with an upper face 14 of the respective casing half 1. As a matter of course, the presence of the pawls 2 in the tape cassette represents that information may be recorded on the length of magnetic tape contained therein.
If the pawls 2 are broken off from the tape cassette subsequent to the recording of an audio signal on the length of magnetic tape contained in the tape cassette of the type equipped with the erasure preventive pawls, an erroneous or premature erasure of the information recorded thereon can be avoided. However, the breakage of the two pawls 2 is complicated and time-consuming. If a subsequent recording of information on the length of magnetic tape in the tape cassette from which the pawls 2 have been broken off is desired, the associated recesses 3 exposed to the outside upon breakage of the pawls 2 must be covered up in any suitable manner, for example, by the use of an adhesive tape, requiring a complicated and time-consuming procedure.
The use of the erasure preventive pawls is not unique to audio tape cassettes, but is also employed in commercially available VHS video tape cassettes. In the VHS video tape cassettes, however, the detecting face of the erasure preventive pawl is somewhat set back inwardly of the video tape cassette and, therefore, if this design is applied to the audio tape cassette, the analog audio deck now in wide use will detect at all times that the tape cassette is no longer available for information recording.
More specifically, the condition in which the tape cassette is available for information recording means that the detecting face (represented by the pawl 2 shown in FIG. 6) must be in flush with the upper face 14 of the tape cassette.